A variety of vehicles are known and used which have a room or a room portion that may be moved from a retracted position while the vehicle is moving over the road and then expanded when the vehicle is stationary in order to provide additional internal space. This type of an arrangement provides adequate space to accommodate users in transit while still keeping the vehicle within governmental regulations that impose width limitations for vehicles on roads and highways. When these vehicles are stationary, they are frequently used for habitation for extended periods of time, and when so used, it is highly desirable to be able to maximize the available living space.
In the past, most vehicles have used two identical hydraulic cylinders combined along the base portion of the expandable room to expand and retract the room. (The cylinders that expand and retract the room are referred to herein as “mechanism cylinders” since they combine with the mechanism that is being moved by the hydraulic power.) In conjunction with the mechanism cylinders, some prior art devices have employed a synchronizing cylinder to keep the mechanism cylinders moving at the same speed and distance. Synchronizing cylinders are generally described in U.S. Pat. Nos. 4,409,884 (Boehringer) and 6,408,736 (Holt et. al.) which are hereby incorporated by reference. In general, prior art synchronizing cylinders make the same volume of fluid move at the same rate of flow to or from each identical mechanism cylinder so that all mechanism cylinders move the same distance at the same speed.
Recently, the length and weight of expandable rooms has increased as recreational vehicle users have desired more square footage inside their vehicles. Because of the increased length and weight of expandable rooms, many recreational vehicle manufactures are now employing four hydraulic mechanism cylinders to expand and retract expandable rooms, rather than two. Typically, one mechanism cylinder is located near each corner of the room so that there are two upper mechanism cylinders and two lower mechanism cylinders. In addition to the increased strength and rigidity provided by using four cylinders instead of two, the four mechanism cylinder arrangement helps to provide a better seal between the room and the recreational vehicle when the expandable room is in its retracted position.
One problem with using four mechanism cylinders is that there is limited space above the ceiling in a recreational vehicle for the two upper mechanism cylinders to be mounted. Because of this limited space, it is desirable for the upper mechanism cylinders to be smaller in diameter than the lower mechanism cylinders while retaining the same stroke length as the lower mechanism cylinders.
Therefore, there is a need for a synchronizing cylinder that provides for the synchronization of mechanism cylinders having different fluid volumes yet are required to travel the same distance.